The present invention is directed to welded suspension members used in vehicle suspension systems, such as stamped and welded vehicle frames, structures and swing arms, and particularly to an improved method for manufacturing such suspension members.
Suspension members used in vehicle suspension systems are often manufactured from sheet metal stampings which are welded together. For example, vehicle frames are sometimes formed from left and right siderails which are formed from welded channels. The siderails are interconnected by cross members which are welded to the siderails. Swing arms used in independent wheel suspension systems for vehicles are another type of suspension member sometimes formed from stamped and welded steel or only from stamped steel. The swing arm has one end which is pivotally attached to the vehicle frame and a second end on which a wheel is mounted. Any bending or deflection of suspension members such as a vehicle frame or a swing arm may adversely affect wheel alignment for the vehicle. Impulse forces on the wheels, such as occur when the wheels strike an object or drop into a hole while the vehicle is moving, are transmitted to the suspension members. For new vehicles having suspension members formed from stamped and welded steel, these forces may cause plastic deformation of the suspension members, even though the forces are within design limits. The deformation occurs at the high stress areas in the suspension members. As the suspension members yield plastically, the metal is cold worked, the yield point increases, and the metal becomes increasingly resistant to further deformation. As a consequence of the plastic deformation of suspension members in new vehicles, wheel misalignment may occur in vehicles having stamped and welded suspension members after the vehicles are driven only a short distance.